The present invention relates to ethylene oxide sterilization process indicators and, more particularly, to chemical indicator inks that are designed to undergo an irreversible color change when exposed to ethylene oxide vapor in the presence of low-temperature steam, and to methods for indicating that an article has undergone ethylene oxide sterilization processing.
Biological and medical operations such as hospitals, medical laboratories and other allied health facilities, which often come in contact with microorganisms and other microbiological agents, employ a variety of technology to control both infection and contamination. While compositions such as germicides, antiseptics and bacteriostats are effective in controlling widespread growth of biological contaminants, they do not go as far as to completely eliminate these agents.
Since many of the materials and instruments that are used in modern hospitals must be kept sterile, but cannot withstand the heat and/or moisture encountered in a conventional steam sterilization process, there is a growing trend towards the use of an alkylating agent as the sterilization agent. The most popular sterilization alkylating agent presently employed is ethylene oxide gas, generally in an admixture with an inert gaseous diluant such as carbon dioxide, nitrogen, tricloromonofluoromethane, dichlorodifluoromethane, and the like. Ethylene oxide gas can be used as a sporicidal and virucidal agent. Consequently, ethylene oxide sterilization processes are often employed to ensure total eradication of microorganisms.
Since ethylene oxide gas readily diffuses through all of the commonly employed packaging materials and is highly effective in killing microorganisms at temperatures well below those required for heat sterilization techniques, it enables efficient sterilization of many items, particularly those made of thermoplastic materials, which cannot withstand heat sterilization. The process generally involves placing an item in a chamber and subjecting it to ethylene oxide vapor. When used properly, ethylene oxide is not only lethal to all known microorganisms at ordinary temperature, but it is also non-corrosive, readily removed by aeration, easily handled and stored, and has a low toxicity to humans.
Known in the art are methods for indicating that an article has undergone ethylene oxide sterilization. For example, U.S. Pat. Nos. 2,998,306 and 3,098,751 teach methods employing water-based and solvent-based chemical indicators, respectively, which undergo an irreversible color change when placed in an ethylene oxide environment. However, the number of color changes available from these indicators is limited. Moreover, the organic solvents employed in some of these chemical indicators present an environmental hazard. Thus, there is a need for chemical indicator inks that exhibit additional color changes upon exposure to ethylene oxide vapor in the presence of low-temperature steam and do not contain high concentrations of volatile organic compounds.